1. Field of the Invention
The present invention relates to an LSI package equipped with an interface module, an interface module and a connection holder, particularly, to an LSI package equipped with an interface module for signal transmission to external wiring of a high-speed signal, an interface module used in the particular LSI package, and a connection holder for holding the connected state between the interface module and an interposer.
2. Description of the Related Art
In recent years, the clock frequency of an LSI has became higher and higher. In the CPU for a personal computer, a clock frequency which is not lower than GHz order is being put into the practical use. However, the pace of improvement in the throughput of the interface between LSIs is moderate, compared with the elevation of the clock frequency, so as to generate a bottleneck in the performance of the personal computer. Such being the situation, research is being conducted in an attempt to improve the throughput of the interface.
In order to improve the throughput of the interface, it is necessary to improve the signal frequency per terminal and to increase the number of terminals. However, if the number of terminals is increased, the areas of the LSI and the package are increased, giving rise to the limitation that the length of the internal wiring is increased so as to make it impossible to operate at high frequencies. Under the circumstances, it is of high importance to increase the signal frequency per terminal. On the other hand, if the signal frequency per terminal is increased, the attenuation of the electric signal is made large so as to increase the influence given by impedance mismatch to the reflection, with the result that a limitation is generated in the line length. Such being the situation, it is necessary to use as a high-speed signal transmission line having the impedance mismatch and the attenuation of the electric signal suppressed as much as possible.
If a transmission line is to be formed accurately on a mounting board, the manufacturing cost is increased. In addition, the conductor loss caused by the dielectric loss and the skin effect is increased in accordance with increase in the transmission speed so as to make it difficult to transmit a signal over a sufficiently long distance. Under the circumstances, a system for performing signal transmission by using an optical signal is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 2004-31455 and “Electronics Society Meeting by Electronic Information Communication Institute, C-3-123, 2003”. It is proposed in these prior art documents that high-speed wiring, which is not mounted on a mounting board, is mounted on an interposer alone, and that the electric signal is converted by an optical element mounted on the interposer into an optical signal by the utilizing photoelectric conversion so as to carry out the signal transmission by using the optical signal.
To be more specific, Japanese Patent Disclosure No. 2004-31455 quoted above teaches an assembly in which an optical element is mounted as a bare chip directly on an interposer substrate, and the optical element on the interposer substrate is optically coupled with the optical waveguide when the interposer is mounted on a mounting board. In this assembly, however, it is said to be difficult to maintain the optical accuracy because of the difference in the thermal expansion coefficients of the mounting board and the interposer. Also, if the optical element is mounted as a bare chip, it is difficult to secure the reliability of the apparatus. It follows that it is necessary to take an appropriate countermeasure. For example, it is necessary to bury the optical element section in a resin which is transparent to the wavelength used for the signal transmission. It is also necessary to employ an extra work of allowing the optical element to be optically coupled with the optical waveguide on the mounting board. It follows that the manufacturing process must be carried out under many limitations so as to increase the manufacturing cost. Further, since it is necessary to separately attach the optical waveguide to the mounting board, the mounting process is made complex, leading to a further increase in the manufacturing cost. It should also be noted that, in the event of the disorder of the optical element, it is necessary to renew the optical element together with the costly LSI used for the signal processing.
An assembly in which an optical part is mounted directly on an LSI package is disclosed in “Electronics Society Meeting by Electronic Information Communication Institute, C-3-123, 2003” quoted above. In this assembly, it is necessary to apply reflow mounting of the LSI package on a mounting board under the state that the optical part is mounted on the LSI package, or it is necessary to apply a reflow mounting of the LSI package on the mounting board, followed by mounting the optical part on the LSI package. It follows that, in the prior art assembly disclosed in this publication, the optical part or the assembly material such as adhesive, which is thermally weak, interferes with the reflow mounting in the stage of mounting the LSI package on the mounting board. Also, since the soldered portions of the parts interfere with each other in the soldering stage, it is necessary to use different kinds of solders differing from each other in melting point, with the result that the mounting procedure is limited so as to give rise to problems in the mounting stage. Further, for holding the position of the optical connector, it is necessary to separately prepare a push holder. In other words, the holder tends to be made bulky by performing the optical connection in the form of a connector.
It should also be noted that, with increase in the frequency of the signal, the power consumption per terminal tends to be increased in general. For example, the CPU used in a personal computer, has increased the power consumption of the LSI to 70 to 80 W in recent years. Such being the situation, an assembly in which a heat spreader and a gigantic heat sink are mounted so as to increase the heat dissipating area and a formed cooling is performed by using, for example, a fan, is included in the signal processing LSI. On the other hand, since it is necessary to shorten the wiring length between the signal processing LSI and the interface module as much as possible as pointed out previously, a spatial allowance for mounting another heat sink for the interface module is eliminated in the case of installing a heat sink for the signal processing LSI.
Under the circumstances, it is considered effective for the heat sink to be shared by the signal processing LSI and the interface module so as to dissipate the heat simultaneously. In such an assembly, however, the upper surfaces of the signal processing LSI and the interface module are required to be exactly flush with each other when the signal processing LSI and the interface module are simultaneously mounted on the interposer. Alternatively, the difference in height between the signal processing LSI and the interface module is required to fall within a prescribed range that is defined strictly. However, it is difficult to practically satisfy these requirements. In addition, since the interface module is soldered in this assembly, too, it is necessary to renew the interface module together with the costly signal processing LSI if the interface module is out of order.